Google Image Search remains one of the most comprehensive imagery resources available. But the sheer amount of imagery that the site indexes creates a problem. More of than not, Google Image Search gets you close to what you're seeking, but it doesn't really help you find exactly what you're looking for.
Now, Google is working to fix that with new filtering options.
For some time, the only filtering available was for "faces." Then, they added a filter for "photos." Now, Google has introduced new filters that enable you to cull the herd of photos even more. Using the new feature, you can constrain your search to "clip art" and "line drawings."
Still, I have to admit that I'm with Tam Vo over at VentureBeat. Even with these new options, the filter that would provide the most value is still conspicuously absent. I remain hopeful that Google Image Search takes a page from Flickr's book and adds the ability to search by Creative Commons licensing.
Until filtering by license information becomes available, Image Search remains a valuable tool for finding images - and with the new filters you have a much better chance of finding what you're seeking - but they're not images you're likely able to use, legally.